Abstract : Understanding what lies behind the apparent usability of direct manipulation style interfaces might not only help in building better interfaces but can also draw attention to possible side effects. With the help of examples from a prototype data manipulation system, this paper pursues a characterization of direct manipulation interfaces as forestalling the need for procedural reasoning, a class of skills that people appear to have difficulty mastering. The concept of direct manipulation in human-computer interaction can refer to anything from the feeling the user gets while interacting with a system to the apparent concreteness of the way objects are visibly represented. The term procedural reasoning has a more precie definition. Sheil states procedural reasoning is the process by which one determines the effect of a set of instructions or, alternatively, the set of instructions that will achieve a particular effect (1981). With such a definition, procedural reasoning is clearly a skill that has much to do with programming but that also has it place in design and analysis in many other domains. In fact, Sheil argues that it is a basic skill that will be required more and more frequently by nonprogrammers to fully exploit programmed devices. Procedural reasoning is also a skill that people appear to have difficulty mastering.